45G THE MULTIPLICATION OP EFFECTS. 



"When, leaving the development of single plants and ani- 

 mals, we pass to that of the Earth's flora and fauna, the 

 course of the argument again becomes clear and simple. 

 Though, as before admitted, the fragmentary facts Palaeon- 

 tology has accumulated, do not clearly warrant us in saying 

 that, in the lapse of geologic time, there have been evolved 

 more heterogeneous organisms, and more heterogeneous 

 assemblages of organisms; yet we shall now see that there 

 must ever have been a tendency towards these results. We 

 shall find that the production of many effects by one cause, 

 which, as already shown, has been all along increasing 

 the physical heterogeneity of the Earth, has further neces- 

 sitated an increasing heterogeneity in its flora and fauna, 

 individually and collectively. An illustration will make this 

 clear. Suppose that by a series of upheavals, occur- 



ring, as they are now known to do, at long intervals, the East 

 Indian Archipelago were to be raised into a continent, and a 

 chain of mountains formed along the axis of elevation. By 

 the first of these upheavals, the plants and animals inhabit- 

 ing Borneo, Sumatra, Xew Guinea, and the rest, would be 

 subjected to slightly-modified sets of conditions. The cli- 

 mate in general would be altered in temperature, in humid- 

 ity, and in its periodical variations; while the local differ- 

 ences would be multiplied. These modifications would af- 

 fect, perhaps inappreciably, the entire flora and fauna of the 

 region. The change of level would produce additional modi- 

 fications; varying in different species, and also in different 

 members of the same species, according to their distance 

 from the axis of elevation. Plants, growing only on the sea- 

 shore in special localities, might become extinct. Others, 

 living only in swamps of a certain humidity, would, if they 

 survived at all, probably undergo visible changes of appear- 

 ance. While more marked alterations would occur in some 

 of the plants that spread over the lands newly raised above 

 the sea. The animals and insects living on these modified 

 plants, would themselves be in some degree modified by 



